Development of novel plastic scintillators based on polyvinyltoluene for the hybrid j-pet/mr tomograph

Figure 22 The influence of molecular weight on the relative light output of plastic scintillators. Filled dots refer to 
samples in which molecular weight were changed by chain transfer agents, while empty dots refer to samples in 
which molecular weight was changed by polymerization temperature. The figure is adapted from [84]. 
Because of the inhomogeneity of macromolecules molecular weight, it is necessary 
to calculate and determine its mean value. There are several methods of mean molecular 
weight description and their determination. In this thesis the viscous mean molecular 
weight was determined. This is one of the most popular methods of macromolecules 
molecular weights determination, which can be applied in the wide range of masses. This 
method is based on the rule that viscosity of polymers solutions is dependent on their 
molecular weight [85].
For the measurements the solution of polystyrene in toluene was prepared. 
Polystyrene was obtained in the same condition as J-PET plastic scintillators. Time of flow 
of solvent (toluene) and solutions with different concentrations of polystyrene between 
points A and B in Ostwald's viscometer (Fig. 23) were measured.
 
 
 
 
 
 
 
Figure 23 Ostwald's viscometer. The picture is adapted from [86].
 

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52 
Each time the viscometer was filled by the same amount of liquid by the right arm, 
to the point denoted as C. Then the liquid was suctioned above point A, and the time 
between reaching lines A and B was measured. 
Then relative viscous (
r
) was determined for solvents of each concentration as: 
r
(6), 
were 
is a viscosity of polymer solution, 
- viscosity of the pure solvent, 
- time of 
polymer solution flow between points A and B of the viscometer, 
- analogues time 
measured for the pure solvent. Specific viscosity was determined as: 
(7), 
and reduced viscosity is equal to: 
red
(8), 
where c denotes polymer concentration. 
Based on the reduced viscosity dependence on the polymer concentration in the solution, 
the intrinsic viscosity [η] was determined by interpolating linear fit to the zero 
concentration. For data presented in Fig. 24, it is equal to 97.4. 
0.001
0.002
0.003
0.004
0.005
0.006
0.007
105
110
115
120
125
130
135
140
y = 6047.6x + 97.4
R
2
= 0.984 
Reduc
ed v
is
co
si
ty
Concentration [g/ml]